Support for Data Type Changes in Iceberg

In many cases, changing data types doesn’t result in data loss. Where Iceberg supports such changes, `dbt-glue` should accommodate them.

This can be achieved by maintaining a **dictionary** mapping which data type changes are allowed. For instance:

```python
supported_type_changes = {
"int": ["bigint", "float"],
"float": ["double"],
"string": ["text", "varchar"]
}
```

A second phase, this could involve implementing a add/drop logic to handle more complex data type changes based on user preferences (even if data is lost). I can provide a detailed specification for this if needed.

The issue does not name any files, tests, or entry points. Start by locating the adapter's existing Iceberg schema-change handling and identify how current and target data types are represented. Done means supported non-lossy type changes are accepted through a defined compatibility mapping; the proposed add/drop behavior is described only as a possible later phase.

Written by the indexing model from the issue text.